This invention relates to the measurement art and, more particularly, to a method and apparatus for measuring the torque and/or horsepower transmitted by a loaded rotating shaft, and also rotary shaft speed.
One common technique for measuring the torque transmitted by a loaded rotating shaft is to cement a strain gage to the surface of the shaft. The strain gage is deformed by twisting of the shaft, which is proportional to the torque exerted on the shaft by the prime mover. The low amplitude output signal from such a strain gage exhibits erratic drift over a period of time due to creep of the cement.
Further, if the strain gage is excited by direct current, slip rings and brushes, which wear with prolonged use, are needed to couple the electrical source and readout to the strain gage, and if the strain gage is excited by alternating current, a transformer is needed to couple the electrical source and readout to the strain gage.
Another technique for measuring the torque transmitted by a loaded rotating shaft employs a torsional variable differential transformer. Although this technique does not use a strain gage on the shaft or slip rings or brushes, it does require a well regulated alternating current excitation source and four balanced pickup coils to detect the change in magnetic permeability of the shaft due to torsional stress therein.
None of the above-described torque meters generates speed information; thus they require an additional sensor, such as a magnetic pickup device, to determine rotary speed (RPM) information for measurement of horsepower. Further, all of the above torgue meters employ analog signal processing and are bulky, thus unbalancing the power shaft and causing excessive bearing wear.